[sc-118386] - Adds proper support to MVT experiments

[vlacerda]

Description

Disclaimer: This PR enables code found here.

(To test you need to run both branches locally and make Opticks a local dependency.)

This PR adds support to MVT tests and simplifies the usage of Optimizely JS SDK. This is achieved through:

Removing the distinction between feature and experiment.

Optimizely's SDK now makes no distinction on their decisionInfo contract, leading to a simplification of code and a need for conventions to be set in place.

Retro-compatible support for on and off

We added temporary retro-compatibility to transforming on and off variants into b and a respectively.
Why we needed this? We used to use the property decisionInfo.enabled to determine which side the customer would fall in a rollout, by using convertBooleanToggleToFeatureVariant to convert enabled:true|false into b or a.
enabled in its turn, on Optimizely's side responds to "On", "Off" automatically. This logic was fine if we had only rollouts. However, enabled is not used on MVT (enabled is boolean, MVT is multivariant).
We had to find a different way to return the variant. Given that now we can set the value of variationKey, we can as well use a, b, c, ... directly into Optimizely's dashboard. This led to a simplification on our code and more intuitive usage of the product.

Shortcut Story

https://app.shortcut.com/findhotel/story/XXXXX

[sc-XXXXX]

How to review/test this change

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